If a target date is set, you can use the special strings ${target_days} or ${target_years} in the event text to display the number of days or years since (or until) that date. You can also use ${target_date} to display the date itself.

For example, if

the target date is May 24, 1941

the event text is "Bob Dylan is ${target_years} years old today", and

the event occurs on May 24th, 2020,

then the event will display as "Bob Dylan is 79 years old today" Or, if:

the target date is June 21, 2020

the event text is "Summer solstice is in ${target_days}", and

the event occurs on April 1, 2020,

then the event will display as "Summer solstice is in 81 days"

This works with repeating events too, so the displayed interval would change based on the date of the repeating instance.